This invention relates to a system and method for using a weighted sweep material for removing particles from a well bore penetrating a possible hydrocarbon producing formation.
A problem often encountered in well-drilling operations is the accumulation of drilling cuttings, especially on the low side of deviated, or horizontal, well bores. As these cuttings accumulate within the well bore, it is necessary to occasionally pump a volume of drilling fluid that has been weighted to a density higher than the active drilling fluid system in order to clean, or sweep, the well of the drilling cuttings. This “weighted sweep” material, which is often in the form of barite, or the like, is introduced into the well bore with the drilling fluid and scours the low side of the well bore to clean the well bore of cuttings. The weighted sweep material also provides extra buoyancy to mobilize and remove the cuttings from the well bore, and the cuttings are then separated from the weighted sweep material by shaker screens, or the like.
Upon completion of the weighted sweep, the weighted sweep material must be removed from the drilling fluid and taken out of the well bore. However, it is virtually impossible to remove all of the weighted sweep material from the well bore. Thus, some of the material will remain in the well bore and become part of the well formation, which may cause several problems. For example, the presence of the non-removable, weighted sweep material could reduce the permeability of the rock being drilled and cause a distortion of the particle size distribution of the bridging materials in the drilling fluid. Also, the presence of the weighted sweep material makes it difficult, if not impossible, to eliminate some plugging of the permeable zones in the formation. Thus, the rock in the drilled pay zone could be damaged, and thus possibly impede the withdrawal of oil and gas.
Therefore, what is needed is a system and method for removing the cuttings from the well bore without encountering the above problems.